Liquid systems, such as coatings, varnishes, emulsion paints and printing inks, are usually colored with paint colorant or other such pigment formulations either by In-Factory or by In-Store methods. In-Factory coloration of paint involves coloring large batches of paint in a factory with select colors. The finished paint is then shipped to shops for direct sale.
By contrast, with In-Store coloration, a consumer purchases white latex or alkyd paint, and then selects a color from a swatch to be matched. A tinter in the form of paint colorant is then metered by a dispensing system directly into the can of paint. Various colorants are metered into the paint in order to achieve the desired color match, and this process is often controlled by computer color matching software. Typically, there are twelve colorants in a dispensing system: six of which are based upon organic pigments and six of which are based upon inorganic pigments. Dosing levels may vary from 1 ounce to 12 ounces per gallon (7-90 g/l) of paint to achieve proper color strength. Once the colorant is dispensed into the can of paint, a paint shaker is used to insure homogeneity.
Paint colorant ordinarily contains pigment, water, inorganic extender, humectants, surfactants and other additives, such as biocides and defoamers. The organic pigment palette can vary, but generally contains phthalocyanine blue (ranging from green shade to red shade), phthalocyanine green, quinacridone magenta, carbazole violet, quinacridone violet, naphthol red and monoarylide yellow. The pigment concentration varies, but the range will typically be from about 5% (for deep colors, such as violet, blue and quinacridone) to up to about 40% (for light colors, such as yellow).
Organic pigments are initially formed in a presscake phase, where the pigment percentage can vary from 20% to over 50% solids with the remainder being water. Presscake can then be dried to 100% powder by various techniques. The techniques can include, but are not limited to, spray drying, spin-flash drying and tray drying. Aggregation or agglomeration occurs with both formation of presscake or dry color; however, it generally occurs to a greater degree with dry color. Therefore, for pigment to be of commercial value in the coloration of paints, inks, plastics and other areas, the pigment dry color or presscake must be dispersed into a suitable medium (water, solvent, oil, wax, plastics, etc.) by use of dispersants and by various milling techniques. Dry color provides larger formulating latitude due to being 100% color; while presscake is more limiting due to the relatively low solids; however, dry color is more difficult to disperse due to high levels of aggregation.
Colorants generally contain inorganic extender in order to build solids, density and viscosity necessary for efficient dispensing. Talc, clay or other suitable extenders are typically used from levels ranging from about 7% up to about 40%. The pigment and extender are dispersed into water with surfactant, and combinations of surfactants may be used for this purpose. Also, surfactants of medium-to-high HLB are preferred for pigment dispersing. Low HLB surfactants or hydrophobic surfactants are also utilized to impart alkyd compatibility to the colorant, since alkyd paints are also colored.
Humectants, such as ethylene glycol, propylene glycol and others are used for a variety of reasons in the colorant. Levels of humectant may range from about 5% to 40% depending upon the system. Humectants provide additional compatibility with the paints, as well as freeze/thaw resistance and reduced flaking once the colorant dries in the can. These are also used as leveling and flow agents in paints. Examples of colorant compositions are described in U.S. Pat. No. 6,488,760. In U.S. Pat. No. 6,582,505 aqueous pigment dispersions are described for the coloration of paints. These contain branched alcohol alkoxylates as pigment dispersants.
There is a need for stir-in pigment powders that have dispersability and color properties similar to liquid paint colorants, but do not require all the additives of current formulations mentioned above and that are easy to store and transport.
Stir-in forms of dry color have been developed. US 2005/0080171 describes a form of stir-in colorant containing 60%-90% by weight of at least one pigment; 10%-40% by weight of at least one nonionic surface-active additive based on polyethers; and 0.1%-10% by weight of at least one anionic surface-active additive based on sulfonates, sulfates, phosphonates or phosphates. These preparations can then be used to pigment macromolecular organic and inorganic materials, such as in the In-Store coloration method. DE 10204304 A1, DE 10227657 A1 and WO 03066743 A1 contain similar compositions with the following surface-active types: non-ionic surfactant based on polyethers, anionic surface-active additive based on sulfonates, sulfates, phosphonates or phosphates. U.S. Pat. No. 6,379,451 describes a pigment composition prepared with a pigment in the presence of a nonionic surfactant composed of acetylenic linkage. These pigment compositions are prepared through dry-milling.